Field of the Invention
The present invention relates to a processing method of a single-crystal substrate such as a sapphire (Al2O3) substrate, a silicon carbide (SiC) substrate, a gallium nitride (GaN) substrate, a lithium tantalate (LiTaO3) substrate, a lithium niobate (LiNbO3) substrate, a diamond substrate, a quartz substrate, or the like.
Description of the Related Art
In an optical device fabrication process, an optical device layer made up of an n-type nitride semiconductor layer and a p-type nitride semiconductor layer is stacked on the front side of a sapphire (Al2O3) substrate, a silicon carbide (SiC) substrate, or a gallium nitride (GaN) substrate, and optical devices such as light-emitting diodes, laser diodes, or the like are formed in a plurality of regions divided by a plurality of division lines formed in a grid pattern on the optical device layer, thereby producing an optical device wafer. Then, a laser beam is applied to the optical device wafer along the division lines to cut the optical device wafer, dividing the regions with the optical devices formed therein thereby to manufacture individual optical devices. A SAW wafer with SAW devices formed on the front side of a lithium tantalate (LiTaO3) substrate, a lithium niobate (LiNbO3) substrate, a silicon carbide (SiC) substrate, a diamond substrate, or a quartz substrate is also cut into individual SAW devices by a laser beam applied to the SAW wafer along division lines.
As a method of dividing wafers such as optical device wafers and SAW wafers as described above, there has been tried a laser processing method that uses a pulsed laser beam having a wavelength which permeates through the workpiece, wherein the pulsed laser beam is applied to the workpiece while positioning a converged point thereof within an area to be divided. A dividing method using such a laser processing method is a technology for dividing a wafer by applying a pulsed laser beam having a wavelength which permeates through the wafer from one surface thereof while positioning a converged point thereof within the wafer thereby to form a succession of modified layers serving as rupture start points along a division line within the workpiece and exerting an external force on the wafer along a street where the strength is lowered by the modified layers (see, for example, Japanese Patent No. 3408805).
Furthermore, as a method of dividing a wafer such as a semiconductor wafer, an optical device wafer, or the like along a division line, there has been put to practical use a technology for performing an ablation process on a wafer by irradiating the wafer with a pulsed laser beam having a wavelength absorbable by the wafer along a division line thereby to form laser-processed grooves, and exerting an external force on the wafer along the division line where the laser-processed grooves have been formed as rupture start points, thereby splitting the wafer (see, for example, Japanese Patent Laid-Open No. Hei10-305420).